The manufacture of appliance cabinets and other parts from steel sheet or strip is a capital-intensive, multi-step process. A simplified recitation of the conventional steps would include forming the incipient housing, cabinet or automotive part from the steel strip, cleaning it, rinsing it, applying a phosphate coating, rinsing again, electrocoating, rinsing, and baking. It should be remembered that housings and cabinet parts for laundry washers and dryers, for example, are large and cumbersome to move in and out of the various coating, drying, immersing and baking areas. In addition, conditions in the electrolytic bath must be monitored and/or controlled. Quality control rejections of large parts such as appliance cabinets can be quite expensive.
Filiform corrosion too often appears between the metal and the final coating, forming iron oxides in thread-like lines emanating from an anodic nucleus where oxygen is able to penetrate through the paint or other coating. To guard against filiform corrosion, phosphate treatment, usually in the form of zinc phosphate, is undertaken to place a phosphate coating on it for corrosion control, but is not entirely effective in that the parts are still undesirably subject to a risk of filiform corrosion.
Such a complicated and demanding process, having many steps and numerous conditions to maintain, necessarily provides many opportunities for error and mishap. The industry would benefit from a simple process with as few steps as possible as well as from obtaining a process which significantly reduces the incidence of filiform corrosion.
Containers made from ECCS (electrocoated chrome/chrome oxide strip, sometimes known as tin-free steel), both three-piece fabricated cans and “D&I”, or drawn and ironed cans, without phosphate coatings, have been proposed for electrocoating in a resin-containing bath. See Seiler U.S. Pat. No. 4,303,488 and Colberg's U.S. Pat. No. 3,939,110, both describing polycarboxylic resins for use in electrocoating of cans acting as the anode. Cans are typically quite thin-walled; conventionally, they are clear lacquered.